Method of producing flocked nonwoven fabric



Aug. 5, 1969 N. s. NEWMAN I METHOD OF PRODUCING FLOCKED NONWOVEN FABRIC Filed April 1, 1965 T M M W United States Patent 3,459,579 METHOD OF PRODUCING FLOCKED N ONWOVEN FABRIC Nicholas S. Newman, West Newton, Mass, assignor to The Kendall Company, Boston, Mass., a corporation of Massachusetts Filed Apr. 1, 1965, Ser..No. 444,536 Int. Cl. Bb 1/02; C09j 5/04 US. Cl. 117-33 2 Claims ABSTRACT OF THE DISCLOSURE This invention relates to nonwoven fabrics with a flocked suede or pile-like surface. More particularly it relates to a process, and the product thereof, wherein the bonding of the textile-length fibers constituting the nonwoven fabric and the bonding thereto of the flock fibers are effected in a continuous operation and by the use of a single adhesive bonding agent.

It has been long known in the art to provide a unified fibrous base sheet, such as a paper, a fabric, or a bonded nonwoven fabric with a coating of adhesive and to deposit onto the adhesive-coated areas, while they are still in a tacky and unset condition, a layer of very short, cut, nontextile length fibers known as flock. Such very short fibers, generally ranging from 0.375 inch down to 0.01 inch in length, are generally applied to unified fibrous bases to enhance all or selected portions of the base by providing a suede-like, velvet-like, or even pilelike surface thereon. Application of the flock is by known conventional methods for which commercial equipment is available, based either on electrostatic deposition such as the Statitron (International Industrial Development Company), or based on a process wherein the flock is dusted or sifted onto an adhesive-coated base which is kept in a vibrating condition by means of for example octagonal beater bars. The particular method of application of the flock is not critical and forms no part of the present invention.

Prior art methods for producing flocked surfaces on non-woven fabrics have involved the steps of (1) assembling a fleece or web of unspun, unwoven textile length fibers; (2) unifying the fibrous web either by impregnation thereof with a bonding agent, or else by heat-andpressure activation of binder fibers present in the web; (3) drying the web if liquid bonder is used, or cooling it if thermoplastic fibers are used, either method leading to the formation of a bonded, self-sustaining nonwoven fabric; (4) applying to the surfaces of the bonded nonwoven fabric, or to selected areas thereof, a second adhesive for the purpose of anchoring the flock; (5) applying flock to the adhesive-coated areas while the adhesive is still tacky, and (6) drying or curing the web to effect positive and permanent anchorage of the flock thereto.

A multi-stage process of this conventional type is time-consuming and expensive, involving the application of two binders and also two drying operations. It is the essence of this invention that I have found that the adhesive or bonding agent used to bind together the textile-length fibers in the nonwoven base material can under certain circumstances be made to serve as the ad- Patented Aug. 5, 1969 ice hesive agent which holds the flock fibers on the surface of the base material. This allows a simpler and more economical process, comprising the steps of: (1) dryassembling an array of textile-length fibers; (2) saturating said array of fibers with a binder of the proper viscosity; (3) applying flock fibers to the surface of the saturated fibrous base while the binder is still tacky; and (4) drying or curing the combination of textile-fiber base and flocked fibers.

In addition to simplicity and economy, the process of this invention has the additional advantage of applying the flock fibers to the fibrous base while the latter is saturated with fluid binder, with the result that the driving action of the electrostatically-impelled flock fibers causes them to penetrate down between the textile fibers of the base, thus fortifying the fibrous structure of the base and providing better anchorage of the flock by such penetration in depth. This effect is described in more detail below.

It is, therefore, an object of this invention to provide an improved process for the preparation of flocked nonwoven fabrics involving the application of a single binder system.

It is a further object of the invention to provide a flocked nonwoven fabric in which textile-length fibers disposed genetrally in a horizontal plane are bonded to each other by a primary bonding agent, said textile length fibers forming a bonded nonwoven fabric which has adherent to the surfaces thereof a coating of flock fibers, disposed generally perpendicularly to the plane of the textile-length fibers and bonded thereto by the same primary bonding agent serving to bond said textile-length fibers to each other.

It is a still further object of the invention to provide a flocked nonwoven fabric of this type in which the flock fibers, disposed generally perpendicularly to the plane of the textile-length fibrous base, penetrate down through said base and between said textile length fibers, and are adhesively united to said textile-length fibers by the same primary binde-r serving to bond the fibers of the base into a nonwoven fabric.

The invention may be bettter understood by reference to the following description and drawings, wherein:

FIGURE 1 represents a cross-sectional view of a typical prior art flocked nonwoven fabric.

FIGURE 2 represents a cross-sectional view of a flocked nonwoven fabric of this invention, and

FIGURE 3 is a schematic representation of a train of equipment suitable for carrying out the process of the invention.

Referring to FIGURE 1, there is shown a prior art flocked nonwoven fabric 10 consisting of a bonded nonwoven fabric base 12, an adhesive coating 14 applied to one face of the nonwoven fabric, and flock fibers 16 deposited on and adherent to the adhesive coating. The fibers '12 of the nonwoven fabric base are shown as bonded to each other by a bonding agent 13, used in the original formation of the nonwoven fabric. The bonding agent 13 not only bonds the textile fibers 12 together, but it occupies a substantial fraction of the void space in the base fibrous layer. The bonded nonwoven fabric base is therefore of a less open and porous nature than the unbonded fibrous fleece of which it was originally composed, and as such it resists penetration by the adhesive layer 14 and by the flock fibers 16. Similar considerations pertain to nonwoven fabrics made by felting or by bonding by means of a thermoplastic fiber content in the base material by use of heat and pressure. In each case the fibers of the base material are brought closer together and interfiber spacing is decreased. As a result, prior art flocked nonwoven fabrics made by the conventional process in which the fibers of the nonwoven layer are bonded prior to the flocking process are generally characterized by a lack of free void space and a degree of rigidity which prevents penetration of the flock into the body of the fibrous base.

For the purpose of this invention, textile-length fibers are defined as those which are of sufiicient length to allow their being processed into a fleece or web by conventional dry-assemblying equipment such as a carding machine, garnett, air-lay machine or the like, such machines depositing fibers generally in a horizontal plane, although the incliniation of fibers to each other within the plane may vary from highly parallelized to isotropic. Any type of textile fibers may be used, including cotton and the natural fibers, rayon, acetate, and the true synthetic fibers derived from man-made polymers. The choice of fiber will be dictated by economics and by the properties of strength, flexibility, etc., which it is desirable to incoporate into the finished product.

Referring to FIGURE 3, a web 21 of dry-assembled textile-length fibers from any convenient source, not shown, is deposited on an endless belt 22, conveniently a fine-meshed screen, driven by drive rolls 24, 24. In its progress along belt 22 the fibrous web 21 is saturated with an appropriate binder mixture 28, as explained below, from an overhead metered spray head 26. If adjustment is needed in the amount of binder delivered to the fibrous web 21, it may be effected by squeeze rolls 30, 30. Thence the saturated web passes under a chamber 32, containing flock fibers 16, said chamber delivering fiock fibers to the web either by gravity dusting or by imparting an electrostatic charge to the short flock fibers, in which case the conveyor belt 22 is conductive and is charged oppositely to the charge imparted to the fiock. The eveness of distribution of the flock on the surface of the fibrous web may be improved by rotating one or more beater bars, 34, conveniently of hexagonal shape, mounted below and in contact with the conveyor belt 22 and serving to vibrate said belt and the supernatant fibrous web. In practicing this invention, the deepest penetration of flock fibers into the fibrous base is realized by the use of beater bars in combination with either gravity flock feed or electrostatic feed. Drying is conveniently effected by an overhead infrared drier 36.

In most operations where flock is deposited onto an adhesive-surfaced substrate, not every flock fiber will be anchored firmly to the adhesive surface. Removal of excess unbound flock may be accomplished by passing the dried flocked Web under a vacuum chamber 42, the action of which is assisted by a rapidly revolving brush roll 38, or a beater bar 40, or by a combination of both. The finished flocked web 20 then passes to a conventional wind-up roll 44.

It will be apparent to those skilled in the art that various alternative types of equipment may be used in certain of the above stages. Saturation of the fibrous web with binder may be carried out by immersion of the web in a trough of binder; pick-up may be adjusted by a vacuum box mounted below the conveyor 22; and drying may be by means of a tunnel dryer.

Referring to FIGURE 2 as a typical product of this invention, the flocked nonwoven fabric 20 is composed of a substrate of textile-length fibers 12, bonded by a bonding agent 18, with the flock fibers 16 penetrating deeply into the underlying substrate, reinforcing it, and being bonded to said substrate by the same bonding agent 18 which serves to bond the long fibers of the substrate together. The penetration of the flock fibers into the base is such that a substantial proportion of the lower ends of said flock fibers penetrate into the base to a depth greater than two thicknesses of the textie, fibers comprising the base. An appreciable number of such flock fibers penetrate completely through the fibrous base, as shown at 17, so that their lower ends project to and are visible from the bottom side of the product.

In order to provide a single binder system capable of unifying both the base fibrous web and the flock into a unitary structure in accordance with this invention, it is necessary that the binder should have a certain minimum viscosity in order for it to permeate the fibrous Web to such an extent that it develops a tacky, adhesive surface at the point where the flock is applied. I have found that a viscosity of between 200 and 5,000 centipoises, as measured by the #2 spinde of a Brookfied viscosimeter at 12 rpm, is a satisfactory operating range when the fibrous base web is saturated with between 25% and 100% of its own weight in binder (on a solids basis), a preferred amount of binder. On a wet basis, this corresponds to between 50% and 200% of a 50% solids binder system.

If the viscosity of the binder system is substantially below 200 centipoises, the binder may be so thin that it is absorbed by and held between the fibers of the fibrous web, so that it is difficult or impossible to maintain a uniform layer of tacky binder on the web surface. Flock applied under such conditions may adhere either poorly or not at all to the base web. Too high a binder viscosity, on the other hand, leads to difficulties in uniform binder application and to lack of uniform penetration into and distribution throughout the fibrous web.

The critical point at which the binder viscosity determines proper bonding of the fibers in the base web to each other and proper anchorage of the flock to the surface of the web lies between the binder-saturation step and the flock-applying step. In using water-based binder, such as the commercially available and commonly used acrylic, vinyl, and synthetic rubber emulsions and latices, the desired minimum viscosity of 200 centipoises may be imparted to the binder system by the use of thickening agents, as illustrated in Example 1 below. When binder systems based on polymers dissolved in low-boiling organic solvents are used, it will be found that at normal processing speeds of 10 to 20 yards per minute there is considerable solvent evaporation, with a consequent development of a viscosity that is substantially higher than the viscosity of the solvent solution as originally applied to the web and a consequently adhesive and tacky web surface during the flocking stage.

The process of this invention is illustrated by the following examples.

Example 1 A carded web of 3 denier l% -inch viscose fibers weighing 30 grams per square yard was saturated with the following water-based binder system and the wet pick-up adjusted to 100% on the weight of the web:

emulsion E214 (Rohm and Haas), a self-crosslinking acrylic emulsion of 45% solids content.

7% of a 3% aqueous solution of a high-viscosity cellulose ether thickening agent (Methocel 4,000, a product of Dow Corporation).

0.7% ammonium chloride, a catalyst promoting crosslinking.

0.06% of an alkylaryl polyether alcohol, as a penetrant.

0.25% of an alkylaryl polyether alcohol dispersing agent, Triton X-l55, a product of Rohm and Haas.

17% water.

The binder system as applied to the fibrous Web had a Brookfield viscosity of 850 centipoises.

Rayon fiock 0.75 millimeter long, 3 denier, was applied to the adhesive-surfaced fibrous web both by electrostatic deposition and by a combination of beater-bar and gravity sifting. The result was in each case a fibrous nonwoven fabric with a suede or plush-like surface, both the fibers of the nonwoven fabric and the flock fibers being bonded into an integral unit by the same binder, and with the flock fibers penetrating down into and reinforcing the base of textile-length fibers. In general, the beater-bar technique was found to deliver about 20 grams of flock to the fibrous web surface, while electrostatic deposition built up a coating of about 40 grams of flock per square yard.

Essentially similar results were obtained in repeating the above procedures using ground cotton as the flock instead of rayon.

Example 2 Using the same rayon web as in Example 1, saturation was carried out using a 100% pick-up of a water-based acrylic latex S7-699 (a product of B. B. Chemicals Cor-v poration), of 27% solids content. The latex as applied had a viscosity of 1675 centipoises. Application of 25 grams of ground cotton per square yard to this base material gave a product resembling the ground cotton samples of Example 1.

Example 3 and 2, and a wet pick-up of 100%, the rayon flock of Example 1 was applied both electrostatically (40 grams per square yard) and by gravity dusting plus beater-bar (20 grams per square yard). The result, as in the previous examples, was a suede-surfaced nonwoven fabric, with flock fibers dispersed throughout the depth of the fibrous base, and oriented generally in a direction perpendicular to the plane of the base.

It is not essentialthat the whole of any surface be flocked, decorative effects being readily realized by printing a desired pattern of binding agent onto the base fibrous array and thereby confining the flocked effect to such selected areas.

Having thus'described my invention, I claim:

1. The method of producing a nonwoven fabric with a flocked surface, said surface consisting of discontinuous, short-length substantially parallelized fibers oriented substantially at right angles to the plane of the fabric, which comprises dry-assembling an unbonded but intermingled array of textile-length fibers, supporting said array while applyingthereto a liquid medium containing a binding agent for said fibers,

applying to said array while still wet with the said liquid medium a coating on at least portions of one face thereof short-length fibers of the type known as flock,

orienting said short-length fibers essentially normally to the planeof said fabric,

causing at least a portion of said short-length fibers to penetrate in depth between said textile-length fibers, and evaporating said liquid medium,

to thereby bind the short-length fibers to said array of textile-length fibers without the use of any secondary binding material.

2. The process according to claim 1 wherein the liquid medium containing the binding agent has a viscosity of between 200 and 2,000 centipoises, as measured at 12 r.p.m. by the #2 spindle of a Brookfield viscosimeter.

References Cited UNITED STATES PATENTS 2,368,706 2/1945 Fountain 117-28 2,859,150 11/1958 Toulmin 117-28 X 1,825,827 10/ 1931 Smith 161-64 2,258,092 10/ 1941 Fogg 11717.5 2,522,527 9/1950 Manning 1l717 X 2,951,005 8/1960 Hervey 11733 X 3,020,169 2/ 1962 Philips et al. 11733 3,322,606 5/1967 Koller 16164 X WILLIAM D. MARTIN, Primary Examiner J U.S. Cl. X.R. 

